1. Field of the Invention
The present invention relates to a fuse structure, and in particular the fuse structure of a third conductive layer, that can avoid damage to the adjacent fuse structure from the laser blow process in the laser spot of the fuse structure.
2. Description of the Related Art
Fuses are routinely used in the design of monolithic integrated circuits (IC), and in particular in memory devices as elements for altering the configuration of the circuitry contained therein. As such, memories are commonly built with programmed capabilities wherein fuses are selectively xe2x80x9cblownxe2x80x9d by a laser beam.
It is well known that random access memories (RAM) are designed with redundancies which include spare columns, rows, or even fully functional arrays, wherein when any of these spare elements fails, the defective row, column and the like are replaced by a corresponding element. Disabling and enabling of spare elements is accomplished by fuses which are blown (i.e., melted away) when required, preferably, by a laser beam.
Additionally, the technique of laser fuse deleting (trimming) has been widely used both in the memory and logic IC fabrication industries, as an effective way to improve functional yields and to reduce development cycle time. Yet, fuse blow yield and fuse reliability have been problematic in most conventional fuse designs.
FIG. 1 is a sectional view of a traditional fuse structure, and FIG. 1 shows a cross section B-Bxe2x80x2 of FIG. 3. FIG. 2 is a sectional view of a traditional fuse structure, and FIG. 2 shows a cross section C-Cxe2x80x2 of FIG. 3. FIG. 3 is a top view of a traditional fuse structure.
Referring to FIG. 1, symbol 100 shows a substrate. A first dielectric layer 120 is formed on the substrate 100. A metal layer M0 is formed on part of the first dielectric layer 120. A second dielectric layer 150 is formed on part of the metal layer M0 and part of the first dielectric layer 120. A metal layer M1 is formed on part of the second dielectric layer 150. At least one conductive plug 130 is defined through the second dielectric layer 150, for electrically connecting the M0 layer and the M1 layer.
Referring to FIG. 2, is a sectional view of a traditional fuse structure, and FIG. 2 shows the cross section C-Cxe2x80x2 of FIG. 3.
FIG. 3 is a top view of FIG. 1 and FIG. 2. There are plural fuse structures 210, 220, 230, 240, 250, 260 in fuse window 140. Each fuse structure comprises the M0 layer, the conductive plug 130 and the M1 layer. The solid line area shows the M1 layer, the dash line area shows the M0 layer, and each structure comprises its own optimal of a laser spot 110. To give an example, a laser beam 296 blows the position 110 of the fuse structure 240. Because of misalignment of the laser beam 290 or thermal scattering of the laser beam 290, thermal shock from the laser blow process can damage the M0 layer. This can cause the fuse structures to crack, seriously affecting device reliability and yield.
Accordingly, an object of the invention is to provide a fuse structure, and in particular a fuse structure of the third conductive layer that can avoid damage to the adjacent fuse structure from the laser blow process in the laser spot thereof.
The present invention provides a fuse structure. An optimal position of laser spot is defined above a substrate. A first dielectric layer is formed on the substrate. A first conductive layer is formed on part of the first dielectric layer. A second dielectric layer is formed on part of the first dielectric layer and part of the first conductive layer. A second conductive layer is formed on part of the second dielectric layer. A third dielectric layer is formed on part of the second conductive layer and part of the second dielectric layer. A third conductive layer is formed on the third dielectric layer and does not electrically connect the first conductive layer and second conductive layer, wherein the third conductive layer and third dielectric layer have an opening to reveal part of the second conductive layer, and define a laser spot of the fuse structure.
At least one conductive plug penetrates the second dielectric layer, to electrically connect the first conductive layer and the second conductive layer, to function as a fuse.
The advantage of the present invention is a third conductive layer placed on top of the second conductive layer. The third conductive layer has an opening to reveal part of the second conductive layer and define a laser spot of the fuse structure.
When a laser beam blows the fuse structure of a laser spot in the second conductive layer, the third conductive layer can obstruct or absorb superfluous laser energy, to prevent damage to the adjacent first conductive layer. The fuse structure of the prior art has no conductive layer or dielectric layer on the top of fuse structure.